1. Field of the Invention
The present invention relates to a driving method for a plasma display unit of a plasma display, and more particularly, to a driving method that uses a resonant circuit to generate a sinusoidal waveform in a reset period to prevent violent discharge of the plasma display unit, to increase the image contrast of the display panel and to decrease the electric power consumption.
2. Description of the Prior Art
The plasma display panel has a large but thin size and does not produce radiation. Therefore, it is believed to be the trend of future large-sized displays. A plasma display panel contains a plurality of plasma display units disposed in a matrix form and filled with a dischargeable gas. A driving circuit follows a driving sequence to drive the plasma display units so as to excite and ionize the dischargeable gas to emit light through its discharge. The circuit characteristic of the plasma display panel is closely equivalent to a capacitor-like load. The driving method is to impose a high voltage and high frequency alternating current on both ends of the capacitor-like load so that the charges in the plasma display unit are driven back and forth. The ultraviolet light radiated during the driving procedure will be absorbed by the fluorescent agents applied on the display cells to emit visible light.
With reference to FIG. 1, a conventional plasma display panel 10 contains a back panel 12 installed in parallel to a transparent front panel 14. A plurality of electrode pairs 16 are installed beneath the front panel 14. Each electrode pair contains two electrodes 18, 19, with each electrode 18, 19 being long and rectangular in shape and having a fixed width. A dielectric layer 20 is formed beneath the front panel 14 and covering the electrode pair 16 to provide the capacitance needed for alternative driving so as to prevent electric breakdown. A passivation layer 22 is formed under the dielectric layer 20, and is usually composed of MgO to protect the dielectric layer 20 from deterioration due to plasma sputtering. The back panel 12 is formed with a plurality of ribs 24, and a plurality of data electrodes 26 between the ribs 24. Blue, red and green phosphors 30B, 30R, 30G are filled, respectively, between each two adjacent ribs 24. Dischargeable gas is filled between the front panel 14 and the rear panel 12 of the plasma display panel 10. The top of the plurality of ribs 24 is fixed under the passivation layer 22 to separate the plasma on both sides of the ribs 24 from communication and interference.
The electrodes 18, 19 of the plasma display 10 are also called the X and Y sustaining electrodes. The X and Y electrodes are wide and nearly-transparent conductors, usually made of indium tin oxide (ITO) to induce and maintain discharging. Beneath the X and Y sustaining electrodes 18, 19 are bus electrodes 36, 38, respectively. The bus electrodes 36, 38 are thin and opaque metal wires, usually made of Crxe2x80x94Cuxe2x80x94Cr, to help the X and Y electrodes 18, 19 to induce discharging and to lower the resistance of the X and Y electrodes 18, 19.
As shown in FIG. 1, the intersection of each two ribs 24 and electrode pair 16 forms a subpixel unit 32B, 32R or 32G. The three subpixel units 32B, 32R, 32G constitute a pixel unit 34. The subpixel units 32B, 32R, 32G and the pixel unit 34 are represented by the areas enclosed by the dashed lines. When a potential difference is applied on the X and Y sustaining electrodes 18, 19 in the subpixel units 32B, 32R, 32G and the data electrodes 26, the X and Y sustaining electrodes 18, 19 and the data electrodes 26 form an electric field to induce discharging of dischargeable gas to produce ultraviolet (UV) light, which is absorbed by the fluorescent agents 30B, 30R or 30G to emit visible light.
With reference to FIG. 2, the driving sequence of a conventional plasma display has the following periods: (a) reset period, (b) address period, (c) sustaining period, and (d) data erase period. In the reset period, the plasma display imposes a large potential difference on the X and Y sustaining electrodes of which the primary purpose is to generate the same amount of wall charges in each of the display units so that image data can be correctly recorded in the subsequent address period. The dischargeable gas in the plasma display unit can be excited and ionized in the sustaining period so as to discharge and result in image display.
In the plasma display panel disclosed in U.S. Pat. No. 6,037,916, a voltage waveform Pc1 is first imposed on the X and Y sustaining electrodes 18, 19 in the reset period of the driving sequence. However, such a voltage waveform is likely to cause instantaneous voltage changes in the plasma display unit. Therefore, some ions at higher energy levels will violently discharge, resulting in self-erase discharges and UV photons absorbed by the fluorescent agents on the display unit. As a result, the plasma display unit emits light of a certain intensity in the reset period when it should emit as little light as possible. Therefore, compared with the sustaining period for displaying images, the intensity contrast is less and cannot be increased.
In observation of the above problem, U.S. Pat. No. 5,745,086 discloses a slow rise and fall voltage waveform to generate wall charges in order to solve the side effect caused by instantaneous voltage waveform changes. A set of rise time control circuit and fall time control circuit produces the needed voltage waveform. The basic principle of the control circuit is to use a constant current source to charge resistor-like elements and the capacitor-like load of the plasma display panel. Then, a properly tuned RC time constant is provided to control the rising and falling speed of the voltage waveform. As well, due to the use of resistor-like elements, some electric power will be wasted on the resistor-like elements. Furthermore, since it uses a constant current power supply, the power source itself consumes energy. Therefore, this technique effectively increases the contrast, but is unable to control energy consumption.
Thus, it is a primary object of the invention to provide a new driving method for the plasma display unit which can effectively generate a sinusoidal waveform by using a resonant circuit so as to prevent the plasma display unit from misfiring, to increase the image contrast of the display panel, and to effectively reduce electrical power consumption.
According to the claimed invention, a driving method for a plasma display panel is used. The plasma display panel has a plurality of plasma display units. Each unit has first and second electrodes forming a capacitor-like load, and a passivation layer formed above the first and second electrodes. The plasma display unit is filled with a dischargeable gas that generates wall charges above the passivation layer after application of a potential difference by a driving circuit. The driving circuit comprises a resonant unit electrically connected to the first electrode of the plasma display unit. During a reset period, the driving circuit charges the resonant unit to produce an electrical potential difference between the two electrodes to form wall charges above the passivation layer. Next, the driving circuit resonates the capacitor-like load of the plasma display unit together with the resonant unit to produce a smooth sinusoidal waveform.
It is an advantage of the present invention that the driving method produces resonance between the resonant unit and the capacitor-like load so as to generate a sinusoidal waveform in the reset period. Since the smooth sinusoidal waveform does not have any abrupt edges, little self-erase dicharges will be generated, improving image contrast. As well, the use of resonance between the resonant unit and the capacitor-like load allows for a decrease in power consumption.
These and other objectives of the present invention will no doubt become obvious to those of ordinary skilled in the art after reading the following detailed description of the preferred embodiment, which is illustrated in the various figures and drawings.